Open Gland Glut

7/31/2019 Open Gland Glut

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Introduction to ComputerGraphics with OpenGL/GLUT


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What is OpenGL?

OpenGL (Open Graphics Library) A software interface to graphics hardware

a standard specification defining a cross-language,

cross-platform graphics rendering API for writing

applications that produce 2D/3D computer graphics. the industry's most widely used, supported and best

documented 2D/3D graphics API.

2


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OpenGL and GLUT

GLUT (OpenGL Utility Toolkit) An auxiliary library

A portable windowingAPI

Easier to show the output of your OpenGL application

Not officially part of OpenGL

Handles: Window creation,

OS system calls

Mouse buttons, movement, keyboard, etc


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How to install GLUT?

Download GLUT http://www.opengl.org/resources/libraries/glut.html

Copy the files to following folders: glut.h VC/include/gl/

glut32.lib VC/lib/ glut32.dll windows/system32/

Header Files: #include

#include

Include glut automatically includes other header files
http://www.opengl.org/resources/libraries/glut.htmlhttp://www.opengl.org/resources/libraries/glut.html


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GLUT Basics

Application Structure Configure and open window

Initialize OpenGL state

Register input callback functions

render resize

input: keyboard, mouse, etc.

Enter event processing loop


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Event Handling in OpenGL/GLUT

You tell OpenGL which user-defined function to callwhen certain events occur.

OpenGL monitors the input devices. When

something happens (mouse down, key press, etc. )

OpenGL calls your code. Can provide functions for

window resizing

mouse button presses

mouse button releases

mouse motion

keyboard presses


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Events in OpenGL

Event Example OpenGL Callback Function

Keypress KeyDown

KeyUp

glutKeyboardFunc

Mouse leftButtonDown

leftButtonUp

glutMouseFunc

Motion With mouse press

Without

glutMotionFunc

glutPassiveMotionFunc

Window Moving

Resizing

glutReshapeFunc

System Idle

Timer

glutIdleFunc

glutTimerFunc

Software What to draw glutDisplayFunc


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GLUT Callback functions

Event-driven: Programs that use windows

Input/Output

Wait until an event happens and then execute

some pre-defined functions according to the usersinput

Events key press, mouse button press andrelease, window resize, etc.

Your OpenGL program will be in infinite loop


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Window Resizing

void glutReshapeFunc(void (*func)(int w, int h)) func is a pointer to a function that takes two arguments,

the new width w and new height h of the window.

OpenGL calls this function whenever the window is

resized. func typically makes a call to glViewport() so that

the display is clipped to the new size, and redefines the

projection matrix so that the aspect ratio of the projected

image matches the viewport.


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Mouse Events

void glutMouseFunc(void (*func)(int button, int state,

int x, int y));

func is a pointer to a function that takes 4 integerparameters. func is called by OpenGL whenever a mousebutton is pressed or released.

button specifies which mouse button was pressed, and iseither:

GLUT_LEFT_BUTTON,

GLUT_RIGHT_BUTTON, or

GLUT_MIDDLE_BUTTON


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Mouse Events

state specifies the state of the mouse button, andis either:

GLUT_UP, or

GLUT_DOWN

x and y specify the location (in window-

relative coordinates) of the mouse whenthe event occurred.


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Mouse Motion

glutMotionFunc( void (*func)(int x, int y));

func is called by OpenGL when the mouse pointer moves

within the window while one or more mouse buttons are

pressed. x and y specify the location of the mouse when

the event occurred.


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Keyboard Events

void glutKeyboardFunc(void (*func)(unsigned char key,

int x, int y));

func is a pointer to a function that takes 3 parameters.func is called by OpenGL whenever a key is pressed.

key is the ASCII value of the key that was pressed

x and y specify the location of the mouse whenthe key was pressed .


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Idle Function

glutIdleFunc( void (*func)());

func is called by OpenGL when no other events are

pending, when it would otherwise be idle.

Pass in Null (0) to disable the function.


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Example Code using OpenGL Input

int main( int argc, char** argv)

{

glutInit(&argc, argv);

glutInitDisplayMode( GLUT_RGB || GLUT_SINGLE );

glutInitWindowSize ( 250, 250 );

glutInitWindowPosition ( 100, 100 );

glutCreateWindow (argv[0]);init ();

glutDisplayFunc ( display );

glutReshapeFunc (reshape );

glutMouseFunc ( mouse );

glutMotionFunc ( motion );glutKeyboardFunc ( keyboard );

glutMainLoop ();

return 0;}


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Example Code Using OpenGL Input

void display ( void ){

glClear ( GL_COLOR_BUFFER_BIT );

glColor3f (1.0, 1.0, 1.0);

glBegin (GL_POINTS);glVertex3f (0.5, 0.25, 0.0);

glVertex3f (0.75, 0.5, 0.0);

glVertex3f (0.75, 0.75, 0.0);

glVertex3f (0.25, 0.75, 0.0);glEnd();

glFlush();

}


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void reshape (){

// called when window is resized.

// typically set viewport,

//set projection matrix, etc.}


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void mouse (int button, int state, int x, int y){

switch (button)

case GLUT_LEFT_BUTTON:

if (state == GLUT_DOWN)

// do something

case GLUT_RIGHT_BUTTON:

// etc., etc.

}


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void motion (int x, int y){

// do whatever is appropriate,

// e.g., move object to point (x, y)

}


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void keyboard(unsigned char key, int x, int y)

{switch (key) {

case s:

// do somethingbreak;case S:

// do something here too

break;case t:

case T: // If you dont want to be case sensitive.

// do something here toobreak;

.

.

.}

}


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Matrix Operations

OpenGL has 4 matrices it uses: GL_MODELVIEW

contains the composite modeling and viewing matrices

GL_PROJECTION contains a matrix for the projection transformation

GL_TEXTURE used for performing operations on the texture (stretching,

moving, rotating, etc.)

GL_COLOR used for color space conversions

Make sure the appropriate matrix is current when you domodeling, viewing, or projections


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Setting the Current Matrix

void glMatrixMode(Glenum mode);

sets the current matrix to be mode

mode is GL_MODELVIEW, GL_PROJECTION,GL_TEXTURE, orGL_COLOR


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Loading the Current Matrix

void glLoadMatrix{fd}( TYPE *m)

loads the array m of TYPE GLfloat orGLdouble to

the current matrix


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Multiplying the Current Matrix

void glMultMatrix{fd}(TYPE *m)

Postmultiplies the current matrix by m, which is of

TYPE GLfloat orGLdouble


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Transformations

Translation:void glTranslate{fd}( TYPE dx, TYPE dy,TYPE dz)

TYPE is GLfloat orGLdouble

The translation is applied to the current matrix makesure the appropriate matrix is current, e.g.,

glMatrixMode(GL_MODELVIEW);

glTranslate(0.3, 0.2, 1.5);

Distances are in world coordinates


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Transformations

Rotation:

void glRotate{fd}(TYPE angle, TYPE dx,

TYPE dy, TYPE dz)

rotates angle about the axis given by (dx, dy,

dz) and the origin



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Transformations

Scale:

void glScale{fd}( TYPE sx, TYPE sy, TYPE

sz)

scales about the origin by (sx, sy, sz)



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Viewing - Parallel

Setting an orthographic view

glOrtho(GLdouble left, GLdouble right,

GLdouble bottom, GLdouble top,

GLdouble zNear, GLdouble zFar)

produces a parallel projection with the clipping volumebeing

[left, right] in the x direction

[bottom, top] in the y direction

[zNear, zFar] in the z direction

Only objects falling in this region will be drawn.

Make sure you call glMatrixMode (GL_PROJECTION);

and usually glLoadIdentity();

before calling glOrtho()


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Viewing - Perspective

Setting a perspective viewgluPerspective (GLdouble fovy, GLdouble aspect

GLdouble near, GLdouble far)

fovy is the angle of the field of view in the xzplane, and must be between 0 and 180.

aspect is the aspect ratio (width / height)

near is the distance from the viewpoint to the

near clipping plane (always positive).

far is the distance from the viewpoint to the far

clipping plane (always positive).


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Camera Set-Up

Used to specify camera position and parameters

void gluLookAt( GLdouble eyex, GLdouble eyey,GLdouble eyez, GLdouble atx, GLdouble aty, GLdoubleatz, GLdouble upx, GLdouble upy, GLdouble upz)

The eye point (eyex, eyey, eyez) is the lookFrom pointThe at point (atx, aty, atz) is the lookAt pointThe up point (upx, upy, upz) is the View Up VectorThis call creates the appropriate matrix and applies it to the current

matrix. Hence, we need to set the current matrix mode:

glMatrixMode(GL_MODELVIEW);glLoadIdentity();gluLookAt(0.0, 0.0, 1.0, 0.0, 0.0,

0.0, 0.0, 1.0, 0.0);


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Creating a Normal Vector

glNormal3{dfi}(TYPE nx, TYPE ny, TYPE nz )

TYPE is GLdouble, GLfloat, or GLint

(nx, ny, nz) are the coordinates of the normal vector

If GL_RESCALE_NORMAL is enabled, normals do nothave to be unit size. The system will normalize them foryou.

Normalization is disabled by default

Can enable by calling eitherglEnable(GL_NORMALIZE)

orglEnable(GL_RESCALE_NORMAL)


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Setting the Normals

glBegin (GL_POLYGON);glNormal3fv(n0);

glVertex3fv(v0);

glNormal3fv(n1);glVertex3fv(v1);

glNormal3fv(n2);

glVertex3fv(v2);

glEnd();


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Lighting

To enable lighting in the scene:glEnable(GL_LIGHTING )

This enables lighting in the scene, but doesnot enable individual lights

To enable each light source:

glEnable(GL_LIGHTi)

where 0 i < GL_MAX_LIGHTS


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Lighting

To set the value of a light source parameter:glLight{if}v(GLenum light, GLenum pname,

TYPE params )

light is the light number of the form GL_LIGHTi,

where 0 i < GL_MAX_LIGHTS

pname specifies the light source parameter to set, and is one ofGL_AMBIENT (RGBA)GL_DIFFUSE (RGBA)GL_SPECULAR (RGBA)GL_POSITION (x, y, z, w) if w = 0, it is a directional light

GL_SPOT_DIRECTION (x, y, z)

params is a pointer to an array that contains the data


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Lighting

To set the ambient lighting in the scene:

glLightModel{if}{v}(

GLenum GL_LIGHT_MODEL_AMBIENT,

TYPE params )

params contains a pointer to 4 int or float values that

specify the ambient RGBA intensity of the entire scene.


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Shading

To set the shading type for the scene:glShadeModel (GLenum mode )

mode specifies the type of shading to be

done, and is either

GL_FLAT

GL_SMOOTH (Gouraud shading)

The default is GL_SMOOTH


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Setting Material Properties

To set the material properties for the current material:glMaterial{fi}{v}(GLenum face, GLenum

pname, TYPE params )

face specifies which face the properties should be

applied to and is:GL_FRONTGL_BACK

GL_FRONT_AND_BACK

GL_BACK is used for shading back-facing

polygons when two-sided lighting is enabled


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Setting Material Propertiespname specifies which parameter is to be set and is:

GL_AMBIENT The ambient reflectance of the material. (RGBA)

GL_DIFFUSE The diffuse reflectance of the material. (RGBA)

GL_SPECULAR The specular reflectance of the material. (RGBA)

GL_EMISSION The emitted light intensity of the material. (RGBA)

GL_SHININESS The specular exponent of the material. (int or float)


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Texture Mapping

Steps in using textures in OpenGL:

1. Create a texture.

2. Indicate how the texture is to be applied toeach pixel.

3. Enable texture mapping.

4. Draw the scene, specifying both texture and

geometric coordinates .


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Creating a Texture

glTexImage2D(GLenum target, GLint level,

GLint internalFormat,GLsizei width, GLsizei height,GLint border, GLenum format,GLenum type, const GLvoid *pixels )

target should be GL_TEXTURE_2D.

level should be 0.

internalFormat should be GL_RGB.

width is the width of the texture (power of 2).

height is the height of the texture (power of 2).

border should be 0.

format should be GL_RGB. type specifies the type of data stored, and should be GL_INT,GL_FLOAT, etc.

pixels is a width by height array of the texture data.


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Naming a Texture Object

In order to use a texture in OpenGL, you need to name it.

The safest way is to have GL provide unused texturenames.

void glGenTextures (GLsizei n, GLuint *textureNames);

Returns n unused names for texture objects in the array textureNames

After creating the texture name, it must be bound to the texture.

void glBindTexture (GLenum target, GLuint textureName)

target should be GL_TEXTURE_2D

This call creates a new texture object with default values for the

texture image and texture properties. Subsequent calls to glTexImage*() glTexParameter*(), etc. store

data in the texture object.


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Setting the Texture Environment

void glTexEnvi (GLenum target, GLenumpname, GLint param);

This call sets the current texturing environmentparameters

target should be GL_TEXTURE_ENV

pname should be GL_TEXTURE_ENV_MODE

param should be GL_DECAL

Other texturing functions are available - look at anOpenGL book for details

These are probably the parameters you want.


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Setting the Texture Parameters

void glTexParameteri (GLenum target,GLenum pname, GLint param);

This call sets the current texturing parameters

target should be GL_TEXTURE_2Dpname should be GL_TEXTURE_WRAP_S orGL_TEXTURE_WRAP_T

param should be GL_REPEAT

Other texturing functions are available, but these are

probably the parameters you want.


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Texture Coordinates

When you draw an object, you need to specify bothgeometric coordinates and texture coordinates foreach vertex.

Textures are interpolated between vertices.

void glTexCoord2{sifd} (TYPE coords);

e.g.,void glTexCoord2f(GLFloat s, GLFloat t);

This call sets the current texture coordinates. Subsequentcalls to glVertex*() have those vertices assigned to the settexture coordinate


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Example of Using Textures

void init (void){

glGenTextures(1, &texName);

glBindTexture(GL_TEXTURE_2D, texName);

glTexParameteri(GL_TEXTURE_2D,

GL_TEXTURE_WRAP_S, GL_REPEAT);

glTexParameteri(GL_TEXTURE_2D,

GL_TEXTURE_WRAP_T, GL_REPEAT);

glTexImage2D(GL_TEXTURE_2D, GL_RGB,width,height, 0, GL_RGB, GL_INT,

texImage);

}


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void display (void){

glEnable(GL_TEXTURE_2D);

glTexEnvi(GL_TEXTURE_ENV,

GL_TEXTURE_ENV_MODE, GL_DECAL);glBindTexture(GL_TEXTURE_2D, texName);

DrawQuad();

glFlush();

glDisable (GL_TEXTURE_2D);

}


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void DrawQuad(void) {

glBegin(GL_QUADS);glTexCoord2f (0.0, 0.0);glVertex3f (-2.0, -1.0, 0.0);glTexCoord2f (0.0, 1.0);glVertex3f (-2.0, 1.0, 0.0);glTexCoord2f (1.0, 1.0);glVertex3f (0.0, 1.0, 0.0);

glTexCoord2f (1.0, 0.0);glVertex3f (0.0, -1.0, 0.0);glTexCoord2f (0.0, 0.0);glVertex3f (1.0, -1.0, 0.0);glTexCoord2f (0.0, 1.0);glVertex3f (1.0, 1.0, 0.0);glTexCoord2f (1.0, 1.0);

glVertex3f (2.414, 1.0, -1.4.1);glTexCoord2f (1.0, 0.0);glVertex3f (-2.414, -1.0, -1.414);

glEnd();

}

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